EP 2 381 198 discloses a method for separating carbon dioxide from a flue gas.
According to EP 2 381 198, flue gas is first compressed and pretreated e.g., to cool it and remove water. The flue gas is then passed through a sequence of heat exchangers (the so called cold boxes) where the flue gas is separated into carbon dioxide rich streams and carbon dioxide lean streams, which are then supplied into a distillation column.
At the distillation column non-condensable gas (e.g. nitrogen, argon, etc.) and carbon dioxide liquid are separated.
The non-condensable gas, after expansion in an expansion valve, is passed through the heat exchangers (cold boxes) to cool them.
The carbon dioxide liquid is further purified in a reboiler, where non-condensable gas is further separated and removed from the carbon dioxide liquid. In this respect the carbon dioxide liquid from the distillation column is passed through a cold side of the reboiler, and already purified carbon dioxide from a high-pressure compressor is passed through a warm side of the reboiler.
The carbon dioxide liquid, from both the warm side of the reboiler and the cold side of the reboiler, is then collected in a buffer drum.
From the buffer drum, the carbon dioxide liquid is expanded and passed through the heat exchangers (cold boxes) to cool them.
At the buffer drum, carbon dioxide evaporation occurs due to the heat exchange through the surface of the buffer drum. In addition, because of the different temperatures of the carbon dioxide liquid from the cold side of the reboiler (e.g. about 0° C.) and warm side of the reboiler (e.g. about 3° C.); these different temperatures cause heating of the colder carbon dioxide liquid against the warmer carbon dioxide liquid thus leading to the risk of evaporation.
Thus, a system and method that counteract risk of carbon dioxide liquid evaporation, after the carbon dioxide liquid has been separated from other non-condensable gas is needed.